(a) The Field of the Invention
The present invention relates to low viscosity unsaturated polyester resins, essentially comprising an unsaturated polyester alkyd and an ethylenically unsaturated monomer copolymerizable with the alkyd. The present invention relates also to the products, particularly buttons in all their marketable forms, obtained from said polyester resins by any processing technique suitable for such a purpose.
(b) The Prior Art
Commercial products called "unsaturated polyester resins", obtained by mixing an unsaturated polyester alkyd with a copolymerizable monomer, are known; the known resins however have a higher viscosity, an inferior workability, a lower luster and an inferior resistance to repeated washings, than the resins of the present invention, the amount of monomer and the elastic modulus and heat distortion temperatures (HDT) of the hardened pure resin being equal. In other words, the applicant has surprisingly found, and this forms an object of the present invention, that it is possible to obtain low viscosity unsaturated polyester resins having a low styrene content, adapted to the production of buttons by the conventional processing techniques. In a non limitative manner, centifugation and casting in bars or flat sheets are indicated as suitable processes.